Pvn H,i I'UitlS

128 mytilid^:.
Anglesea, in the line of strong currents, enveloped in
similar nests. Dr. Gray has observed that " it creeps
with the foot on the surface of the water, with the shell
downwards like a Cyclas, and it has the power, like that
genus, of crawling up the smooth surface of glass or
china."" The old northern writers called it " anatum
cibus," its littoral habitat rendering it a tempting prey
to wild- fowl. According to Fabricius it is eaten, al-
though seldom, by
the Greenlanders.
The meaning of the specific name has reference to
the opposite direction in which the two sets of ribs or
stria? appear to diverge. It is to be regretted that this
discordance has extended to the synonymy. Montagu
called the present species Mytilus discrepans ; and more
than ten years afterwards Lamarck used the same name
for Modiolaria marmorata, as well as for M. impacta,
a tropical shell.
4. M. ni'gra*, Gray.
Modiola nigra, Gray, Supp. to App. to Parry's First Voyage to the North
Pole, p. ccxliv. Crenella nigra, F. & H. ii. p. 202, pi. xliv. f. 5, and
(animal) pi. Q.
f. 7.
Body " of a transparent white hue, with the margin of the
cloak and siphon tinged with pink, and speckled with brown
and opaque white." (Alder.)
Shell oval, inclining to oblong, compressed, rather thin,
moderately glossy and slightly iridescent: sculpture, about a
dozen remote ribs on the anterior side, and 50-60 close-set
and thread-like ribs on the other side, which latter become
finer towards the middle of the shell ; ventral area not de-
pressed, but without ribs ; transverse striae numerous, coarse,
and flexuous, sometimes forming tubercles or a rough network
where they intersect the longitudinal ribs : colour
purplish-brown : epidermis rather thick, fawn-colour in the
young, olive-green at a subsequent stage of growth, and dark
* Black.